COMPOSITIONS COMPRISING BRÖNSTEDT ACIDS AND MONOAMINES

Description

[0001] The present invention relates to compositions containing strong Brønsted acids, processes for their preparation, and their use. Since the compositions according to the invention are particularly suitable as catalyst compositions, in particular for the curing of epoxy resins, the present invention also relates to catalyst preparations containing strong Brønsted acids.

[0002] Epoxy resins, especially those made from bisphenol A and epichlorohydrin, are well-known raw materials for the production of high-quality casting resins, coating compounds, composites, and adhesives. Aromatic epoxy resins cured with polyamines exhibit good chemical and solvent resistance as well as good adhesion to many substrates.

[0003] Catalysts can be used to accelerate the curing of epoxy-amine coating systems (US 3,492,269 A, US 5,470,896 A, GB 1,105,772 A).

[0004] EP 0 083 813 A1, EP 2 957 584 A1, US 5,441,000 A, US 5,629,380 A, WO 96 / 09352 A1 disclose the catalyzed curing of epoxy resins with various amines.

[0005] US 8,980,979 B2 discloses the curing of an epoxy resin with, among other things, a cyclic diamine selected from piperazine or homopiperazine, optionally in the presence of a catalyst.

[0006] EP 0 969 030 A1 discloses epoxy / amine coating systems whose amine component is an aliphatic amine. The compositions may contain a catalyst.

[0007] US 4,775,734 A discloses the curing of epoxy resins with aminoethylpiperazine using catalytic amounts of tetrafluoroborate or hexafluorophosphate salts of various amines. Comparative examples (Example 2) also disclose an attempt to cure epoxy resins with aminoethylpiperazine in the presence of lithium tetrafluoroborate. However, at the ratio of epoxy groups to NH groups used, no reaction occurs. Another example (Example 14) discloses the reaction of ammonium hexafluorophosphate with diethylamine.

[0008] US 5,134,239 A discloses adducts of heterocyclic nitrogen-containing compounds and salts. Example 58 discloses, as a non-inventive example, the synthesis of a butylamine-tetrabutylphosphonium fluoroborate complex in methanolic solution.

[0009] WO 2017 / 074810 A1 discloses compositions comprising an epoxy resin, a polyetheramine and a further amine hardener, which may be, inter alia, an aliphatic amine, and optionally a metal triflate catalyst.

[0010] The applications EP 3 569 629 A1, EP 3 569 630 A1, EP 3 569 631 A1 and EP 3 569 632 A1 disclose compositions comprising at least one epoxy resin, at least one cyclic amine having at least two amino groups and at least one salt of a Brönsted acid.

[0011] It is desirable to accelerate the curing of epoxy formulations with catalysts in order to save energy and reaction time. Salts of strong Brønsted acids (i.e., those with a pKa value of less than or equal to 2), and especially salts of very strong Brønsted acids (i.e., those with a pKa value of less than or equal to -9.01), have proven particularly suitable. However, their disadvantage is that they are solids and difficult to homogenize in liquid epoxy formulations. Prior dissolution or dispersion in solvents is also disadvantageous – dispersing or dissolving the catalysts in inert solvents increases the VOC (volatile organic content) of the epoxy compositions. Reactive solvents, on the other hand, lead to precipitation, discoloration, and reduced reactivity.

[0012] It is therefore the object of the present invention to provide compositions which contain the salts of strong Brönsted acids which are very suitable as catalysts for epoxy formulations and which do not have the aforementioned disadvantages.

[0013] Surprisingly, it was found that salts of strong or very strong Brønsted acids, especially salts of trifluoromethanesulfonic acid (triflates), dissolve well in primary aliphatic monoamines. Surprisingly, it was found that primary aliphatic monoamines dissolve these salts much better than secondary aliphatic monoamines or other monoamines.

[0014] The present invention thus relates to compositions consisting of a) at least one metal, ammonium or phosphonium salt, a Brönsted acid with a pKa value of less than or equal to 2 and b) at least one primary aliphatic monoamine, wherein the compositions comprise 10-95% by weight of component a) and 5-90% by weight of component b), based on the initial weights of components a) and b). More preferably, the compositions comprise 30-70% by weight of component a) and 70-30% by weight of component b), based on the initial weights of components a) and b), even more preferably 40-60% by weight of component a) and 60-40% by weight of component b), based on the initial weights of components a) and b).

[0015] The compositions according to the invention contain at least one metal, ammonium, or phosphonium salt of a strong Brønsted acid. Corresponding salts are good catalysts. Such a strong acid is understood here to be an acid whose pKa value (or, in the case of polyprotic acids, its pKa value of the first protolysis stage) is less than or equal to 2. The pKa of the corresponding acid is preferably less than or equal to -2.

[0016] The pKa is defined as the negative decimal logarithm of the equilibrium constant Ks and is considered a measure of the strength of an acid. The lower the pKa value, the stronger the acid. The pKa value is determined as disclosed in F.G. Bordwell, "Equilibrium Acidities in Dimethylsulfoxide Solution," Acc. Chem. Res. 1988, 21, 456-463.

[0017] Preferred salts are the corresponding salts of the strong acids summarized in the first column of Table 1 below: Table 1: acid pK a value Reference, if not disclosed in Bordwell oxalic acid 1,5 Bayer Walter, Textbook of Organic Chemistry, 21st edition, Hirzelverlag 1988, p. 324 p-toluenesulfonic acid 0,7 Römpp Encyclopedia of Chemistry, 10th edition, Georg Thieme Verlag, Stuttgart, New York, Verlag 1999, pp. 4580-1. Trifluoroacetic acid 0,2 Bayer Walter, Textbook of Organic Chemistry, 21st edition, Hirzelverlag 1988, p. 272 Tetrafluoroboric acid -0,4 e-EROS Encyclopedia of Reagents for Organic Synthesis, Pages 1-4, Conference; General Review; Online Computer File, 2001 nitric acid -1,4 Hollemann Wiberg, Textbook of Inorganic Chemistry, 91st-100th edition, Walter der Gruyter Verlag, Berlin, New York, 1985, p. 603. sulfuric acid -3 Römpp, Encyclopedia of Chemistry, 9th edition, Georg Thieme Verlag, Stuttgart, New York 1991, p. 3459. hydrochloric acid -8 Hydrobromic acid -9 Perchloric acid -10 Hollemann Wiberg, Textbook of Inorganic Chemistry, 91st-100th edition, Walter der Gruyter Verlag, Berlin, New York, 1985, p. 428 Trifluoromethanesulfonic acid -14 hydrogen iodide -9,5 Journal of Physical Chemistry A, Volume 120, Issue 20, Pages 3663-3669. Hexafluorophosphoric acid -10 http: / / www.periodensystem-online.de / index.php?sel=wertdesc&prop=pKs-Werte&show=list&id=acid Hexafluoroantimonic acid -17 http: / / www.periodensystem-online.de / index.php?sel=wertdesc&prop=pKs-Werte&show=list&id=acid

[0018] The salt is preferably the salt of a very strong acid, where such a very strong acid is understood to mean an acid whose pKa value (or, in the case of polybasic acids, its pKa value of the first protolysis step) is less than or equal to -9.01. The pKa value of the very strong acid is preferably between -9.5 and -25, particularly preferably between -9.9 and -21.

[0019] Very particularly preferably, component a) is a salt of a Brönsted acid selected from perchloric acid, trifluoromethanesulfonic acid, hydrogen iodide, hexafluorophosphoric acid and hexafluoroantimonic acid.

[0020] Even more preferably, the salt is a triflate, i.e. a salt of trifluoromethanesulfonic acid.

[0021] Strong Brønsted salts are metal, ammonium, or phosphonium salts. Metal salts include both salts containing metal ions (i.e., containing at least one ion derived from at least one metal, preferably containing an ion derived from at least one metal atom, particularly preferably containing exactly one ion derived from at least one metal atom) and metal-containing ions (i.e., also containing non-metallic components). The counterions of the acids mentioned are thus selected from metal ions, metal-containing ions, phosphonium ions, and ammonium ions.

[0022] Preferred metal ions are alkaline earth metal cations, especially beryllium, magnesium, calcium, strontium and barium ions, as well as lithium, aluminum, bismuth, zinc and europium ions.

[0023] Metal-containing ions are ions that contain at least one metal but are not pure metal ions. These are preferably metal compound ions, such as tetraphenylstibonium ions.

[0024] Ammonium ions can be unsubstituted (= NH 4 +< ), alkylated, and / or arylated. Phosphonium ions can be unsubstituted (= PH 4 +< ), alkylated, and / or arylated. The preferred ammonium ion is NH 4 +< . The preferred phosphonium ion is PH 4 +< . Ammonium ions are particularly preferred.

[0025] Preferred salts of strong acids are calcium triflate, europium triflate, barium triflate, aluminum triflate, bismuth triflate, lithium triflate, lithium perchlorate, barium perchlorate, lithium hexafluorophosphate, and zinc perchlorate. Calcium triflate, europium triflate, lithium hexafluorophosphate, and lithium perchlorate are particularly preferred.

[0026] The best results are achieved with calcium triflate.

[0027] The compositions further comprise at least one primary aliphatic monoamine. In this case, a primary aliphatic monoamine is understood to mean a primary monoamine (i.e., an amine with only one primary amino group) with exclusively aliphatic, i.e., linear or branched alkyl radicals, cycloalkyl radicals, and / or (cyclo)alkyl radicals. (Cyclo)alkyl radicals are understood to mean radicals with both cyclic and linear or branched alkyl moieties. Preferred aliphatic radicals each have 3 to 30, particularly preferably 3 to 10, and very particularly preferably 3-6 carbon atoms. The monoamines may be substituted by a hydroxy radical on one of their alkyl, cycloalkyl, and / or (cyclo)alkyl radicals. However, no other substituents are present. Furthermore, all aliphatic radicals of the monoamine are preferably unsubstituted.

[0028] Monoamines having a boiling point (measured at 1013.25 hPa) of 30 - 300 °C, preferably 30 - 200 °C, are preferably used.

[0029] Most preferably, the monoamine is selected from the group consisting of n-propylamine, iso-propylamine, n-butylamine, iso-butylamine, sec-butylamine, tert-butylamine, n-pentylamine, n-hexylamine and ethanolamine.

[0030] Even more preferred is the monoamine n-butylamine.

[0031] The best results are achieved when component a) is calcium triflate and component b) is n-butylamine.

[0032] The present invention further relates to a process for preparing the composition according to the invention, in which a) at least one metal, ammonium or phosphonium salt of a strong Brönsted acid and b) at least one aliphatic monomine, optionally in the presence of further components, are mixed together.

[0033] The present invention furthermore relates to the use of a composition according to the invention as a catalyst composition. The compositions according to the invention are particularly suitable as catalyst compositions for curing epoxy resins, most preferably for curing epoxy resins with amines. Examples Example 1)

[0034] To demonstrate the special reactivity of the claimed catalysts, model experiments are compared. For this purpose, 0.025 mol (3.75 g) of 1,2-epoxy-3-phenoxypropane is added to a mixture of 22.7 g of toluene (solvent) and 2.08 g of tetradecane (internal standard). 0.025 mol (2.13 g) of piperidine is added, along with 0.06 g of calcium triflate dissolved in the same amount of amine or alcohol as a reference. Immediately after mixing, a GC analysis is performed, and the 1,2-epoxy-3-phenoxypropane content is compared with that of the tetradecane. After 4 h at room temperature (RT), the residual 1,2-epoxy-3-phenoxypropane (EP) content is determined by GC analysis (calibrated using the internal standard tetradecane). The following results are obtained: Comparison of catalysts

[0035] Amine or alcohol Residual % EP in the 0 sample Residual % EP after 4 hours at RT 1 No amine or alcohol 97 0 2 Butylamine 78 3 3 Hexylamine 75 4 4 Octylamine 76 4 5 3-Methylpropylamine 83 4 6 2-Ethylhexylamine 78 5 7 2-Ethylpropylamine 85 6 8 n-Pentylamin 77 2 9 Ethanolamine 78 8 See 1 Ethanol 89 32 See 2 Ethylene glycol 89 32 See 3 Propanediol 86 46 See 4 Butanediol 96 31 See 5 Ethylenediamine 90 33

[0036] The claimed monoamines are suitable as solvents for calcium triflate and do not lead to any significant decrease in reactivity (residual EP content after 4 hours: maximum 10%). Pure alcohols, dialcohols, or diamines, in contrast, lead to a significant decrease in reactivity.

Claims

1. Composition consisting of a) at least one metal salt, ammonium salt or phosphonium salt of a Brønsted acid having a pKA not higher than 2 and b) at least one primary aliphatic monoamine, wherein the compositions have 10-95% by weight of component a) and 5-90% by weight of component b), based on the weights of components a) and b).

2. Composition according to Claim 1, characterized in that the salt a) is a salt of an acid selected from the group consisting of oxalic acid, p-toluenesulfonic acid, trifluoroacetic acid, tetrafluoroboric acid, nitric acid, sulfuric acid, hydrochloric acid, hydrobromic acid, perchloric acid, trifluoromethanesulfonic acid, hydrogen iodide, hexafluorophosphoric acid and hexafluoroantimonic acid.

3. Composition according to either of the preceding claims, characterized in that the Brønsted acid has a pKA not higher than -9.01.

4. Composition according to any of the preceding claims, characterized in that the monoamine b) has exclusively aliphatic radicals having 3-30 carbon atoms.

5. Composition according to any of the preceding claims, characterized in that the monoamine b) has a boiling point, measured at 1013.25 hPa, of 30-300°C.

6. Composition according to any of the preceding claims, characterized in that the amine b) is selected from the group consisting of n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, n-pentylamine, n-hexylamine and ethanolamine.

7. Composition according to any of the preceding claims, characterized in that the salt a) of the Brønsted acid is calcium triflate and monoamine b) is n-butylamine.

8. Process for preparing a composition according to any of Claims 1-7, in which a) at least one metal salt, ammonium salt or phosphonium salt of a Brønsted acid having a pKA not higher than 2 and b) at least one primary aliphatic monoamine are mixed with one another.

9. Use of a composition according to any of Claims 1-7 as catalyst composition.

10. Use of a composition according to Claim 9 as catalyst composition for the curing of epoxy resins.